Powder metallurgical processes offer an alternative to casting and casting-and-working for the production of metallic articles. In a powder metallurgical process, the alloy that is to constitute the article is first prepared in a fine-particle form. A mass of the alloy particulate is compacted to the required shape at elevated temperature with or without a binder. For example, hot isostatic pressing is a binderless process used to manufacture a number of aerospace and other types of parts. Where they can be used, powder metallurgical processes offer the advantages of a more-homogeneous microstructure in the final article, and reduced physical and chemical contaminants in the final article.
The powder used in the powder metallurgical process is typically produced by a method in which the precursor metal of the powder contacts the ceramics in melting crucibles or powder-production apparatus. The result is that the metallic powder particles are intermixed with a small fraction of fine ceramic particles. The presence of the ceramic particles may be acceptable or unacceptable, depending upon the size, composition, and volume fraction of ceramic particles that are present.
When a batch of powder material is received by the manufacturer of the final article from the manufacturer of the powder, the batch may be evaluated as to whether it is acceptable or unacceptable for use in the manufacturing of the final article. One test that may be used to make this evaluation requires that the ceramic fraction of the particles be separated from the metallic fraction, and that the ceramic fraction be analyzed for size and composition of the individual particles. Flotation separation techniques involve mixing a particulate feed into a fluid of the proper density, so that the lighter ceramic particle fraction floats, and the heavier metallic particle fraction sinks. Currently available flotation fluids with the required high specific gravity to achieve this flotation separation include toxic elements such as the thallium component of Clerici's Reagent. An alternative separation technique uses a nontoxic ferrofluid with an applied magnetic field to create a density gradient in the fluid to effect a similar separation. Available ferrofluidic separation devices are complex in structure and fragile. Because of their internal complexity, there are many places for the particles to be trapped within the devices. The result is that the devices are difficult to clean between runs, leading to a significant chance of cross-contamination from one run to the next.
There is a need for an improved approach to the separation of particle fractions, as required for the analysis of the particles and other purposes. The present invention fulfills this need, and further provides related advantages.